Just thought I'd update people to my impressions. Keep in my I am new to higher level headphones, so I think the 'wow' factor probably overshadows everything! Anyhow, being receiverless these last days has lent itself well to exploring the 595's. My friend also let me borrow his 650's for comparison.
The short of it: I can definitely tell a difference between them, even without an amp on the 650. But am I unhappy? Not in the least, since both headphones are simply stunning. As in, holy crap!
The major difference in my mind was that the 650 seems to be able to distinguish between noises better, so that the soundstage was just super super super clear. You could just hear even the most minute detail. Th 595 did a very good job of it, but on some tracks it was just a tad more.. grainy? That's gotta be the wrong word, because it sounds negative, and the 595's were still really excellent. In terms of sound though, I had a hard time telling any other differences (so far).
The only other thing was that the 650's sat better on my head and ears, but that was probably because they have been broken in a bit better.
Anyhow, I am very happy with the 595's and I don't think I would have spent the extra $250 on 650's if I had the option after doing the comparison. But now I have desktop amps running around my brain...
